The present invention relates to polymers having O-substituted vinylphenol unit which is usable as a component of resist, and to resist compositions containing them.
In recent years, quarter-micron pattern formations have been demanded with the increase in the integration level of semi-conductor integrated circuits. Particularly, the eximer laser lithography has attracted attention because it enables producing 64 M to 1G DRAM (dynamic random access memory). As a resist suitable for such eximer laser lithography process, a resist utilizing the chemical amplification effects of an acid catalyst, generally called chemical amplification type resist, has been proposed and is putting in the practical use. For example, in the negative working chemical amplification type resist, an acid is generated from an acid generator by the action of high-energy radiation such as electromagnetic waves, and the solubility of a part exposed to a high-energy radiation of an alkali-soluble resin in an alkaline developing solution is reduced by cross-linking and hardening by the action of the generated acid and a cross-linking agent. On the other hand, the acid does not generate in a part that is not exposed to a high-energy radiation and thus the solubility in the alkaline developing solution is maintained. By such a mechanism, a negative working pattern is obtained by a series of treatments, i.e., a formation of a resist film, an irradiation for patterning and an alkaline development.
Conventionally, polyvinylphenol has been used in most cases as a resin for a chemical amplification type resist. Since, however, polyvinylphenol has a too high solubility in alkaline developing solutions, they have a problem that the sensitivity and the resolution are insufficient. In order to resolve such a problem, use of a polyvinylphenol in which phenolic hydroxyl groups are partly converted to alkyl ethers have been disclosed in JP-A-7-295220 and JP-A-10-69082.
While the use of a polyvinylphenol in which phenolic hydroxyl groups are partly converted to alkyl ethers allows improvement in the sensitivity and the resolution, there is a limit of about 0.22 .mu.m for the resolution particularly of negative working resists. Therefore, improvement has been demanded in this respect. In addition, there is a demand for improvement in the profile (shape of pattern). Moreover, the facts are naturally required that the performance is not changed by the variation of period from the time of coating and drying a resist solution on a substrate to the time of exposing to rays., in other words, the storage stability after coating and before light-exposure is excellent; and that a change in the performance is not significant during a long term storage of a resist composition itself, in other words, the storage stability of the resist composition itself is acceptable.
The purpose of the present invention is to provide a novel polymer which gives an excellent resolution and profile when used as a resin component in a resist composition and gives an acceptable result for the sensitivity, film-forming rate, the coating property, the storage stability after coating and before light-exposure and the storage stability of resist composition itself. The purpose of the present invention is also to provide a resist composition having an excellent performances as described above, using such polymer. As the result of extensive studies for attaining such a purpose, the present inventors have successfully completed the present invention.